Anterior cruciate ligament (ACL) injuries are common among a young, active population. While some individuals can maintain knee stability during daily and sporting activities following ACL rupture (copers), the majority of patients experience knee instability (non-copers). With our early work, we have shown that we can identify those individuals with the potential for dynamic knee stability (potential copers) early after injury. Our work of the past 5 years has also demonstrated that different levels of dynamic knee stability result in changes in movement and muscle patterns, which appear early after injury. Our previous work has demonstrated a rehabilitation program that includes purposeful perturbation of support surfaces (perturbation training) results in superior short-term return to functional activity and improved movement and muscle patterns in potential copers compared to a treatment consisting of standard rehabilitation techniques. Several questions remain that impact the development of effective rehabilitation programs for patients after ACL rupture. How do different levels of dynamic knee stability impact the outcomes over time among active patients with ACL rupture? Are the strategies stable? And how does perturbation training affect movement patterns and recovery of potential copers who eventually undergo surgery? The overall goal of this work is to identify those with better dynamic stability of the knee after anterior cruciate ligament rupture, enhance these patterns with rehabilitation and improve outcomes after reconstructive surgery. The specific aims of this study are to compare clinical and functional outcomes, and the movement and muscle patterns of patients with different levels of dynamic knee stability after participating in perturbation enhanced rehabilitation. Comparisons will be made between potential copers and non-copers before and after training. Patient comparisons after surgery will be performed at the University of Delaware. Patients will not undergo surgery in Norway, allowing us to study the long-term non-operative management of patients with different levels of dynamic knee stability. Results from this study will allow us extend our previous findings and will provide information that is needed to identify and treat individuals with ACL rupture across the spectrum of compensation strategies.